“Generally, the reason that a search space is large is because the possibilities are produced by forming combinations of simpler elements—the individual moves in chess, the city-to-city hops in the traveling salesman problem. This combining of elements leads to a combinatorial explosion of possibilities—an explosion that grows exponentially with the number of elements being combined. Since the possibilities are built from combinations of elements, there is a sense of distance in the space; combinations that share common elements are “closer” than the combinations that do not.”